Method of making a high density integral test probe

ABSTRACT

A high density integrated test probe and method of fabrication is described. A group of wires are ball bonded to contact locations on the surface of a fan out substrate. The wires are sheared off leaving a stub, the end of which is flattened by an anvil. Before flattening a sheet of material having a group of holes is arranged for alignment with the group of stubs is disposed over the stubs. The sheet of material supports the enlarged tip. The substrate with stubs form a probe which is moved into engagement with contact locations on a work piece such as a drip or packaging substrate.

FEILD OF THE INVENTION

[0001] The present invention is directed to probe structrues for testingof electrical interconnections to integrated circuit devices and otherelectronic components and particularly to testing integrated circuitdevices with high density area array solder ball interconnections athigh temperatures.

BACKGROUND OF THE INVENTION

[0002] Integrated circuit (IC) devices and other electronic componentsare normally tested to verify the electrical function of the device andcertain devices require high temperature burn-in testing to accelerateearly life failures of these devices. Wafer probing is typically done attemperatures ranging from 25 C. to 125 C. while typical burn-intemperatures ramge from 80 C. to 140 C. Wafer probing and IC chipburn-in at elevated temperatures of up to 200 C. has several advantagesand is becoming increasingly important in the semiconductor industry.

[0003] The various types of interconnection methods used to test thesedevices include permanent, semi-permanent, and temporary attachmenttechniques. The permanent and semi-permanent techniques techniques athatare typically used include soldering and wire bonding to provide aconnection from the IC device to a substrate with fan out wiring or ametal lead frame package. The temporary attachment techniques includerigid and flexible probes that are used to connect the IC device to asubstrate with fan out wiring or directly to the test equipment.

[0004] The semi-permanent attachment techniques used for testingintegrated circuit devices such as wire bonding to a leadframe of aplastic lead chip carrier are typically used for devices that have lownumber of interconnections and the plastic leaded chip carrier packageis relatively inexpensive. The device is tested through the wire bondsand leads of the plastic leaded chip carrier and plugged into a testsocket. If the integrated circuit device is defective, the device andthe plastic leaded chip carrier are discarded.

[0005] The semi-permanent attachment techniques used for testingintegrated circuit devices such as solder ball attachment to a ceramicor plastic pin grid aray package are typically used for devices thathave high number of interconnections and the pin grid array package isrelatively expensive. The device is tested through the solder balls andthe internal fan out wiring and pins of the pin grid array package thatis plugged into a test socket. If the integrated circuit device isdefective, the device can be removed from the pin grid array package byheating the solder balls to their melting point. The processing cost ofheating and removing the chip is offset by the cost saving of reusingthe pin grid array package.

[0006] The most cost effective techniques for testing and burn-in ofintegrated circuit devices provide a direct interconnection between thepads on the device to a probe sockets that is hard wired to the testequipment. Contemporary probes for testing integrated circuits areexpensive to fabricate and are easily damaged. The individual probes aretypically attached to a ring shaped printed circuit board and supportcantilevered metal wires extending towards the center of the opening inthe circuit board. Each probe wire must be aligned to a contact locationon the integrated circuit device to be tested. The probe wires aregenerally fragile and easily deformed or damaged. This type of probefixture is typically used for testing integrated circuit devices thathave contacts along the perimeter of the device. This type of probecannot be used for testing integrated Circuit devices that have highdensity area array contacts. Use of this type of probe for hightemperature testing is limited by the probe structure and material set.

[0007] High temperature wafer probing and burn-in testing has a numberof technical challenges. Gold plated contacts are commonly used fortesting and burn-in of IC devices. At high temperatures, the gold platedprobes will interact with the solder balls on the IC device to form anintermatallic layer that has high electrical resistance andl brittIemechanical properties. The extent of the intermetallic formation isdependant on the temperature and duration of the contact between thegold plated probe and the solder balls on the IC device. The gold-tinintermatallic contamination of the solder balls has a further effect ofreducing the reliability of the flip chip interconection to the ICdevice. Another problem caused by the high temperature test environmentis diffusion of the base metal of the probe into the gold plated on thesurface. The diffusion process is accelerated at high temperatures andcauses a high resistive oxide layer to form on the surface of the probecontact.

OBJECT OF THE INVENTION

[0008] It is the object of the present invention to provide a probe fortesting integrated Circuit devices and other electronic components, thatuse solder balls for the interconnection means. Another object of thepresent invention is to provide a probe that is an integral part of thefan out wiring on the test substance or other printed wiring means tominimize the contact resistance of the probe interface.

[0009] A further object of the present invention is to provide anenlarged probe tip to facilitate alignment of the probe array to thecontact array on the IC device for wafer probing.

[0010] An additional object of the present invention is to provide anenlarged probe tip to facilitate on the probe surface to inhibitoxidation, intermetallic formation, and out-diffusion of the contactinterface at high temperatures.

[0011] Yet another object of the present invention is to provide asuitable polymer material for supporting the probe contacts that has acoefficient of thermal expansion that is matched to the substratematerial and has a glass transition temperature greater than 200 C.

[0012] Yet a further object of the present invention s to provide aprobe with a cup shaped geometry to contain the high temperature creepof the solder ball interconnection means on the integrated circuitdevices during burn-in testing.

[0013] Yet an addition object of the present invention is to provide aprobe with a cup shaped geometry to facilitate in aligning the solderballs on the integrated circuit device to the probe contact.

SUMMARY OF THE INVENIION

[0014] A broad aspect of the claimed invention is an apparatus forelectrically testing a work piece having a plurality of electricallyconductive contact locations thereon having: a substrate having a firstsurface and a second surface: a plurality of first electrical contactlocations of the first side; a plurality of probe tips disposed on thefirst contact locations; each of the probe tips having an elongatedelectrically conductive member projecting from an enlarged base, thebase being disposed on said contact locations; and, means for movingsaid substrate towards the work piece so that the plurality of probetips are pressed into contact with plurality of contact locations onsaid work pieces.

[0015] Another broad aspect of the present invention is a methodincluding the steps of: providing a substrate having a surface; shearingsaid elongated conductor from said ball bond leaving an exposed end ofsaid elongated conductor, and flattening the exposed end.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] these and other objects, features, and advantages of the presentinvention will become apparent upon further consideration with thedrawing figures, in which:

[0017]FIG. 1 shows a cross section of a high density integral rigid testprobe attached to a substrate and pressed against the solder balls on anintegrated circuit device.

[0018]FIG. 2 shows an enlarged cross section of a single high densityintegral rigid test probe attached to the fan out wiring on the testsubstrate.

[0019] FIGS. 3-7 show the proccesses used to fabricate the high densityitegral rigid test probe structure on a fan out wiring substrate.

[0020]FIG. 8 shows an alternate embodiment of the high density integralrigid test probe structure with a cup shaped geometry surronding theprobe contact.

[0021]FIG. 9 shows an alternate embodiment of the high density integralrigid test probe with multiple probe arrays on a single substrate.

[0022]FIG. 10 shows the structure of FIG. 1 with contact locations on asecond surface.

[0023]FIG. 11 shows the structure of FIG. 6 with conductive pins at thecontact locations on the second surface.

[0024]FIG. 12 schematically shows the structure of FIG. 1 in combinationwith a means for moving the probe into engagement.

DETAILED DESCRIPTION OF THE INVENTION

[0025]FIG. 1 shows a cross section of a test substrate (10) and highdensity integral rigid test probe (12) according to the presentinvention. The test substrate (10) provides a rigid base for attachmentof the probes structures (12) and fan out wiring from the high densityarray of probe contacts to a larger grid of pins or otherinterconnection means to the equipment used to electrically test theintegrated circuit device. The fan out substrate can be made fromvarious materials andl constructions including single and multi-layerceramic with thick or thin film wiring, silicon wafer with thin filmwiring, or epoxy glass laminate construction with high density copperwiring. The integral rigid test probes (12) are attached to the firstsurface (11) of the substrate (10). The probes are used to contact thesolder bralls (22) on the integrated circuit device (20). The solderballs (22) are attached to the first surface (21) of the integratedcircuit device (20).

[0026]FIG. 2 shows an enlarged cross section of the high densityintegral rigid test probe (12). The probe tip is enlarged (13) toprovide better alignment tolerance of the probe array to the array ofsolder balls (22) on the IC device (20). The integral rigid test probe(12) is attached directly to the fan out wiring (15) on the firstsurface (11) of the substrate (10) to minimize the resistance of theprobe interface. The probe geometry includes the ball bond (16), thewire stud (17), and the enlarged probe tip (13). A sheet of polymermaterial (40) with holes (41) corresponding to the probe positions isused to support the enlarged tip (13) of the probe geometry. It isdesirable to match the coefficient of thermal expansion for the polymersheet (40) material and the substrate material to minimize stress on theinterface between the ball bond (16) and the fan out wiring (15). As anexample, the BPDA-PDA polyimide can be used with a silicon wafersubstrate since both have a coefficient of thermal expansion (TCE) of 3ppm/C. This material is also stable up to 350 C.

[0027]FIG. 3 shows the first process used to fabricate the integralrigid test probe. A thermosonic wire bonder tool is used to attach ballbonds (16) to the first surface (11) of the rigid substrate (10). Thewire bonder tool uses a first ceramic capillary (30) to press the ballshaped end of the bond wire against the first surface (11) of thesubstirite (10). Compression force and ultrasonic energy (31) areapplied through the first capillary (30) tip and thermal energy isapplied from thle wire bonder stage through the substrate (10) to bondthe ball shaped end of the bond wire to the first surface (11) of thesubstrate. The bond wire is cut, sheared, or broken to leave a smallstud (17) protruding vertically from the ball bond (16).

[0028] A first sheet of polymer material (40) with holes (41)corresponding to the probe locations on the substrate is placed over thearray of wire studs (17) as shoown in FIG. 4. The diameter of the holes(41) in the polymer sheet (40) is slightly larger than the diameter ofthe wire studs (17). A second shect of metal or a hard polymer (42) withholes (43) corresponiding to the probe locations is also placed over thearray of wire studs (17). The diameter of the holes (43) in the metalsheet (42) is larger than the diameter of the holes (41) in the polymersheet (40). The enlarged ends of the probe tips are formed using ahardened anvil tool (50) as shown in FIG. 5. Compression force andultrasonic energy (51) are applied through the anvil tool (50) to deformthe ends of the wire studs (17). The size of the enlarged probe tip (13)is controlled by the length of the wire stud (17) protruding through thepolymer sheet (40), the thickness of the metal sheet (42), and thediameter of the holes (43) in the metal sheet (42). The enlarged ends ofthe probes (13) can be formed individually or in multiples depending onthe size of the anvil tool (50) that is used. Also, the surface finishof the anvil tool(50) can be modified to provide a smooth or texturedfinish on the enlarged probe tips (13). FIG 6 shows the high densityintegral rigid test probe with the metal mask (42) removed from theassembly.

[0029]FIG. 7 shows the sputtering or evaporation proces used to depositthe desired contact metallurgy (18) on the enlarged end (13) of theprobe tip. Contact metallurgies (18) such as Pt, Ir, Rh, Ru, and Pd canbe deposited in the thickness range of 1000 to 5000 angstroms over theprobe tip (13) to ensure low contact resistance with thermal stabilityand oxidation resistance when operated a elevated temperatures in air. Athin layer of TiN, Cr, Ti, Ni, or Co can be used as a diffusion barrier(19) between the enlarged probe tip (13) and the contact metallurgy (18)on the surgace of the probe.

[0030]FIG. 8 shows a high density integral test probe (12) with anadditional sheet of polyimide (44) with enlarged holes (45)corresponding to the probe location placed on top of the first sheet ofpolyimide (40). The enlarged holes (45) in the second sheet of polyimide(44) acts as a cup to control and contain the creep of the solder ballsat high temperatures.

[0031] Multiple probe arrays can be fabricated on a single substrate(60) as shown in FIG. 9. Each array of probes is decoupled from theadjacent arrays by using separate polyimide sheets (61,62). Matchedcoefficients of thermal expansion for the plymer sheets (61,62) and thesubstrate (60) become increasingly more important for multiple arrays ofprobes on a large substrate. Even slight differences in the coefficientof thermal expansion can result in bowing of the substrate or excessivestresses in the substrate and polymer material over a large areasubstrate.

[0032]FIG. 10 shows the structure of FIG. 1 with second contactlocations (70) on surface (72) of substrate 10. Contact locations (70)can be the same as contact locations (13). FIG. 11 shows the structureof FIG 6 with elongated (74) such as pins fixed to the surface (76) ofpad (70).

[0033]FIG. 12 shows substrate (10) disposed spaced apart from the ICdevice (20). Substrate (11) is held by arm (78) of fixture (80). The ICdevice (20) is disposed on support (82) which is disposed in contactwith fixture (80) by base (84). Arm (78) is adapted for movement asindicated by arrow (86) towards base (84) so that probe tips (12) arebrought into engagement with conductors (22). An example of an apparatusproviding a means for moving substrate (10) into engagement with the ICdevice (20) can be found in U.S. Pat. No. 4,875,614.

[0034] While we have described our perferred embodiments of ourinvention, it will be understood that those skilled in the art, both nowand in the future, may make various improvements and enhancements whichfall within the scope of the claims which follow. These claims should beconstructed to maintain the proper protection for the invention firstdisclosed.

What is claimed is:
 1. An apparatus for electrically testing a workpiece having a plurality of electrically conductive contact locationsthereon comprising: a substrate having a first surface and a secondsurface; a plurality of first electrical contact locations on said firstside; a plurality of probe tips disposed on said first contactlocations; each of said probe tips having an elongated electricallyconductive member projecting from an enlarged base, said base beingdisposed on said contact locations: means for moving said substratetowards said work piece so that said plurality of probe tips ireCpressed into contact with said plurality of contact locations on saidwork piece.
 2. An apparatus according to claim 1 wherein said probe tipis formed from a material selected from the group consisting of Cu, Au,Al, Pd and Pt, and their alloys.
 3. An apparatus according to claim 2wherein said probe tip has at least one coating selected from the groupconsisting of Pt, Ir, Rh, Ru, Pd, Cr, Ti, TiN, Zr, ZrN and Co.
 4. Anapparatus according to claim 2 wherein said protuberance has a firstcoating selected from the group consisting of Cr, Ti, TiN, Ni, Zr, ZrNor Co and a second coating over said first coating selected from thegroup consisting of Pt, Ir, Rh, Ru and Pd.
 5. An apparatus according toclaim 1 , wherein said substrate further includes a decouplingcapacitor.
 6. An apparatus according to claim 1 , wherein said elongatedmember has a flattened end.
 7. An apparatus according to claim 1 whereinsaid second surface has a plurality of second electrical contactlocations thereon.
 8. An apparatus according to claim 1 , wherein saidsecond contact locations have an elongated electrical conductor attachedthereto.
 9. An apparatus according to claim 1 wherein said substrate haselectrical conductor patterns extending from said first surface to saidsecond surface.
 10. An apparatus according to claim 1 , furtherincluding a sheet of material having a plurality of openings, saidopening being positioned to align wtith said plurality probe tips, saidsheet is disposed over said plurality of probe tips, said elongatedelectrically conductive members being disposecd in said opening.
 11. Anapparatus according to claim 10 wherein said elongated electricallyconductive member has a first end disposed in contact with said enlargedbase and a second end disposed in contact with an enlarged tip.
 12. Anapparatus according to claim 10 wherein said sheet is disposed betweensaid enlarged base and said enlarged tip.
 13. An apparatus according toclaim 10 , further including a layer or material disposed on said sheet,said layer having openings aligned with said probe tipts.
 14. Anapparatus according to claim 13 , wherein openings in said layer arelarger than said probe tip.
 15. An appaaratus according to claim 14 ,wherein said contact locations on said Nvork piece are ball-shaped andwherein said openings in said layer are adapted to receive said contactlocation on said work piece having said ball shape.
 16. A structurecomprising: a substrate having a surface; a plurality of electricallyconductive members disposed on said surface; said electricallyconductive members have an enlarged base, an elongated electricallyconductive member in contact with said base and extending away from saidbase; a sheet of material having a plurality of openings disposed foralignment with said plurality of electrically conductive members; saidsheet is disposed over said plurality of electrically conductive memberswith said elongated electrically conductive member extending throughsaid plurality of openings.
 17. An apparatus according to claim 16Nwherein said elongated electrically conductive member has a first enddisposed in contact with said enlarged base and a second end disposed incontact with an enlarged tip.
 18. An apparatus according to claim 16wherein said sheet is disposed between said enlarged base and saidenlarged tip.
 19. An apparatus according to claim 16 . further includinga layer of material disposed on said sheet, said layer having openingsaligned with said probe tips.
 20. An apparatus according to claim 19 ,wherein openings in said layer are larger than said probe tip.
 21. Anapparatus according to claim 20 wherein said contact locations on saidwork piece are ball-shaped and wherein said openings in said layer areadapted to receive said contact location on said work piece having saidball shape.
 22. A structure according to claim 16 wherein said structureis an apparatus for electrically testing a work piece having a pluralityof electrically conductive contact locations thereon.
 23. A structurecomprising: a substrate having a surface; a plurality of electricallyconductive members disposed on said surface; said electricallyconductive members have an elongated base, an elongated electricallyconductive member in contact with said base and having an end extendingaway from said base; said end being enlarged.
 24. A method comprisingthe steps of: providing a substrate having a surface; bonding anelongated electrical conductor to said surface by forming a ball bond atsaid surface; shearing said elongated conductor from said ball bondleaving an exposed end of said elongated conductor; flattening saidexposed end.
 25. A method according to claim 24 , further including thesteps of: providing a sheet of material having an opening therein;disposing said sheet with respect to said surface so that said elongatedconductor extends within said opening.
 26. A method according to claim25 , further including disposing on said sheet a layer of materialhaving an opening therein through which said elongated electricallyconductive member is exposed.
 27. A method according to claim 24 .further including the step of moving said substrate towards a work pieceso that said plurality, of elongated electrical conductors are placedinto electrical contact with a plurality of electrical conductors on awork piece.
 28. A method according to claim 24 wherein said elongatedelectrical conductor is formed from a material selected from the groupconsisting of Cu, Au, Al, Pd and Pt, and their alloys.
 29. A methodaccording to claim 28 further including disposing said exposed end atleast one coating selected from the group consisting of Pt, Ir, Rh, Ru,Pd, Dr, Ti, TiN, Zr, ZrN and Co.
 30. A method according to claim 28further including disposing on said exposed end a first coating selectedfrom the group consisting of Cr, Ti, TiN, Ni, Zr, ZrN or Co anddisposing a second coating over said first coating selected from thegroup consisting of Pt, Ir, Rh, Ru and Pd.
 31. A method according toclaim 24 further including disposing on said substrate a decouplingcapacitor.
 32. A method according to claim 24 wherein said elongatedelectrical conductors are ball bonded to electrical contact locations onsaid surface.
 33. A method according to claim 24 wherein said substratehas another surface having a plurality of electrical contact locationsthereon.
 34. A method according to claim 33 wherein said contactlocations on said another surface have elongated electrical conductorattached thereto.
 35. A method according to claim 24 wherein saidsubstrate has electrical conductor patterns therein.
 36. An apparatusfor making electrical contact with a plurality of solder balls on anintegrated circuit device comprising: first fan out substrate having afirst surface; said first surface having a plurality of contactlocations; a plurality of ball bonds attached to said plurality ofcontact locations; a plurality or short studs extending outward fromsaid ball bonds, away from said first surface on fan out substrate. 37.An apparatus according to claim 36 , further including an enlargedcontact surface at the end of said studs.
 38. An apparatus according toclaim 36 , wherein said plurality of ball bonds and short studs aresurrounded by a layer of polymer material.
 39. An apparatus according toclaim 38 , wherein said polymer material has a coefficient of thermalexpansion that is matched to the first fan out substrate and has a glasstransition temperature greater than 200 C.
 40. An apparatus according toclaim 37 , wvberein said enlarged contact surface has a first metallayer deposited to inhibit oxidation and diffusion of the interface attemperatures up to 200 C; said first metal layer includes a materialselected from the group consisting or Pt, Lr, Rh,. Ru and Pd.
 41. Anapparatus according to claim 41 , wherein a second layer of metal isused between said enlarged contact surface and said first metal layer toprevent out-diffusion of the underlying material; said second metallayer includes a material selected from the group consisting of to TiN,Cr, Ni, and Co.
 42. An apparatus according to claim 39 , wherein saidfan out substrate is selected from the group consisting of mullilayerceramic substrates with thick film wiring; multilayer ceramic substrateswith thin film wiring; metallized ceramic substrates with thin filmwiring; epoxy glass laminate substrates with copper wiring; and, siliconsubstrates with thin film wiring
 43. An apparatus according to claim 38, wherein a second layer of polymer material with enlarged holescorresponding to the said plurality of contact locations is placed oversaid first layer of polymer material and aligned with said enlargedcontact surfaces to form a cup shaped geometry. Y0995-023 19